[vtkusers] How get pixel data in VTK?

[Mark Wyszomierski]

Are you sure you actually set any of the RGB components in the first place?
You could just be allocating the image array, all elements are set to zero,
and you'll just get a zero for every element you access.

Mark

On Thu, Apr 24, 2008 at 12:49 PM, <yenanqu at scs.fsu.edu> wrote:

> when I do
> "unsigned char *pVtkPix = (unsigned char *)pImgData->GetScalarPointer();"
> it doesn't seem to get the scarlar pointer, I have already do all the
> update thing before this, and I also could get dimensions from pImgData. but
> when I output all the RGB value with your method, they are all 0.
> this stuff really kills me~~~
>
>
> Yenan
>
>
> Quoting Mark Wyszomierski <markww at gmail.com>:
>
>  I think the RGB pixel data is usually allocated like:
>>
>>    RGBRGBRGB etc....
>>
>> so you have numPixels * 3 actual elements in your image data array.
>>
>> You get a pixel pointer as usual and cast it to (unsigned char*):
>>
>> // Get a pointer to the actual pixel data.
>> unsigned char *pVtkPix = (unsigned char *)pImgData->GetScalarPointer();
>>
>> // These are the r,g and b values for the first pixel:
>> int rr  = pVtkPix[0];
>> int gg = pVtkPix[1];
>> int bb = pVtkPix[2];
>>
>> // For the second pixel:
>> rr  = pVtkPix[3];
>> gg = pVtkPix[4];
>> bb = pVtkPix[5];
>>
>> and so on. Make sure you don't have RGBA data, if you do, then you just
>> have
>> an extra index per pixel which is the alpha component. Let me know if that
>> helps,
>>
>> Mark
>>
>>
>> On Wed, Apr 23, 2008 at 7:08 PM, <yenanqu at scs.fsu.edu> wrote:
>>
>>  Hi, Mark, I did have the data that is three component. Your example only
>>> shows how to get pixel data that is one component which I never got in my
>>> code before. Do you have any idea how to retrieve this three component
>>> data?
>>> I have try bunch of methods, but none of them is working. any help will
>>> be
>>> greatly appreciated.
>>>
>>> Yenan
>>>
>>> Quoting Mark Wyszomierski <markww at gmail.com>:
>>>
>>>  Hi,
>>> >
>>> > It's definitely possible to get the scalar value from a vtkImageData
>>> > object. You need to know the type of data your object is stored in
>>> > though, for example you'll have difficulty getting the scalar value if
>>> > your data is three component RGB and you're trying to get a single
>>> > pixel scalar pixel value.
>>> >
>>> > I have an example of getting the pixel value that the mouse moves over
>>> > in an image here:
>>> >
>>> >
>>> >
>>> http://devsample.org/index.php?option=com_content&task=view&id=48&Itemid=27
>>> >
>>> > which may help.
>>> >
>>> > Mark
>>> >
>>> >
>>> > On Thu, Mar 27, 2008 at 1:37 PM,  <yenanqu at scs.fsu.edu> wrote:
>>> >
>>> > > Hi, all,
>>> > > I found bunch of the VTK methods to retrieve pixel data from vtk
>>> > > object, such as
>>> > > GetPixelData, GetRGBACharPixelData, etc, but none of them is working,
>>> > > Does anyone know how to get pixel data from VTK object? Thanks in
>>> > > advance.
>>> > >
>>> > > Yenan
>>> > >
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